Investigators located the nine improvised explosive devices near the western edge of The Woodlands in the area of FM 2878 and Woodlands Parkway.

The devices are made from small plastic bottles filled with chemicals and foil or metal objects. A chemical reaction occurs when the devices are shaken and thrown, resulting in the violent rupture of the plastic containers, Williams said.

The acid bombs may contain a clear or foaming liquid and aluminum foil. The reaction is generally short-lived and the bottle may even appear to be bulging. They can easily cause serious injury or property damage.

The injured resident "saw a bottle and reached down to pick it up and it went off in his hand," Williams said. The devices can take anywhere from a few seconds to a few minutes to explode.

They are often left by the side of the road or thrown against a house or door. If one is spotted, residents should not touch the device and instead call 911.

Some "good old-fashioned police work" led to the suspects, Williams said.

"They (officers) combed the area and uncovered some evidence that led to where they got the stuff," he said.

Investigators tracked down video of the suspects buying some of the materials used to make the devices. They appear to be young teens and are likely to be residents of the area, Williams said.

Anyone with information about the case is asked to call the Montgomery County Fire Marshal's Office at 936-538-8288, or Montgomery County Crime Stoppers at 800-392-7867 (STOP). Tips also may be made one at www.montgomerycountycrimestoppers.org. All callers may remain anonymous.